Production of optical recording medium

Abstract

A process for producing an optical recording medium, comprising heat-treating an optical recording medium formed of a thin metal film on the minutely roughened surface of a plastic substrate, the medium being capable of strongly absorbing laser light of a specific wavelength region thereby being able to be written upon.

What is claimed as new and desired to be secured by letters patent of the united states is: 
     
       1. A process for producing an optical recording medium, which comprises: laminating a thin metal film ranging in thickness from 5 to 200 nm onto the minutely toughened surface of a plastic substrate; and   heat-treating said laminated structure at a temperature which is greater than 40° C. and which at the same time is a temperature within the range of a temperature 80° C. lower than the glass transition temperature of the plastic substrate to a temperature 60° C. higher than the glass transition temperature of the plastic substrate; said optical recording medium upon exposure to laser light of a specific wavelength region, being deformed by the formation of bubbles on the thin metal layer of the recording medium which provide for the recording of information.   
     
     
       2. The process for producing an optical recording medium as claims in claim 1, wherein said heat treating is conducted for not less than 1 minute and not more than 120 minutes. 
     
     
       3. The process for producing an optical recording medium as claimed in claim 2, wherein the heat treatment is performed at a temperature higher than 40° C. and within a range where the lower end is lower by 20° C. than the glass transition point of the plastic substrate and the upper end is higher by 60° C. than the glass transition point of the plastic substrate. 
     
     
       4. The process for producing an optical recording medium as claimed in claim 3, wherein the heat treatment is performed at a temperature higher than 40° C. and within a range where the lower end is lower by 20° C. than the glass transition point of the plastic substrate and the upper end is higher by 40° C. than the glass transition point of the plastic substrate. 
     
     
       5. The process for producing an optical recording medium as claimed in claim 4, wherein the heat treatment is performed at high humidity. 
     
     
       6. The process for producing an optical recording medium as claimed in claim 4, wherein the heat treatment is performed on a flat plate. 
     
     
       7. The process for producing an optical recording medium as claimed in claim 23, wherein the plastic substrate has such a regularly roughened surface structure that the regular pitch, measured in the direction parallel to the average surface level, is smaller than the wavelength of the laser light used for writing and reading, and the depth is 0.05 to 1 μm. 
     
     
       8. The process for producing an optical recording medium as claimed in claim 23, wherein the thin metal film is produced from a metal having a melting point higher than 400° C. 
     
     
       9. The process for producing an optical recording medium as claimed in claim 8, wherein the thin metal film is produced from platinum, gold, aluminum, chromium, titanium, iron, nickel, silver, or copper, or an alloy thereof. 
     
     
       10. The process for producing an optical recording medium as claimed in claim 1, wherein the optical recording medium, before writing, has a reflectivity of 5 to 60% when it is struck with laser light through the plastic substrate. 
     
     
       11. The process for producing an optical recording medium as claimed in claim 1, wherein the minutely roughened structure on the substrate surface is formed by injection molding a plastic material. 
     
     
       12. The process for producing an optical recording medium as claimed in claim 1, wherein the minutely roughened structure on the substrate surface is formed by injection compression molding a plastic material. 
     
     
       13. The process for producing an optical recording medium as claimed in claim 1, wherein the minutely roughened structure on the substrate surface is formed by compression molding a plastic material. 
     
     
       14. The process for producing an optical recording medium as claimed in claim 1, wherein the minutely roughened structure on the substrate surface is formed by the photopolymer (2P) process. 
     
     
       15. The process for producing an optical recording medium as claimed in claim 1, wherein the metal layer is protected with a protective layer. 
     
     
       16. The process for producing an optical recording medium as claimed in claim 1, wherein the plastic material of the substrate is a thermoplastic resin. 
     
     
       17. The process for producing an optical recording medium as claimed in claim 16, wherein the thermoplastic resin is a polyester resin, a polyolefin resin, a polyamide resin, a polycarbonate resin, or a polymethacrylate resin. 
     
     
       18. A process for making permanent recordings on the optical recording medium of claim 1, which comprises: causing a semiconductor laser beam to strike the plastic substrate, thereby inducing the local decomposition of the plastic substrate which causes gas evolution that forms bubbles which have increased reflectivity.